For the rapid and effective diagnosis and treatment of infectious diseases, it is desirable to be able to detect the bacteria causing the disease as rapidly as possible. Infections of the urinary tract are among the most common bacterial diseases, second in frequency only to infections of the respiratory tract. In fact, in many hospitals, urinary tract infections are the most common form of nosocomial infections, often following the use of indwelling catheters and various surgical procedures. Most urinary tract infections (UTI) result from ascending infection by microorganisms introduced through the urethra and vary in severity from an unsuspected infection to a condition of severe systemic disease. Such infections are usually associated with bacterial counts of 100,000 (10.sup.5) or more organisms per mL of urine, a condition referred to as significant bacteriuria. Under normal conditions, urine is sterile, although contamination from the external genitalia may contribute up to 1,000 (10.sup.3) organisms per mL in properly collected and transported specimens.
Significant bacteriuria may be present in a number of pathological conditions involving microbial invasion of any of the tissues of the urinary tract, or may result from simple bacterial multiplication in the urine without tissue invasion. The infection may involve a single site such as the urethra, prostate, bladder, or kidney, although frequently it involves more than one site. Infection restricted to the urine may present itself as asymptomatic bacteriuria, i.e., a condition which manifests no overt signs or symptoms of infection. Early treatment of this condition can prevent the development of more serious conditions, e.g., pyelonephritis (inflammation of the kidney and the renal pelvis). The rapid detection of bacteria by a reliable method would therefore facilitate an early and specific diagnosis.
Further, in order to insure that a prescribed antibiotic is in fact effective in treating an infection, repeated tests during therapy are required. The need for simple, rapid bacteriuria tests is thus clear. Moreover, in view of the frequent unsuspected asymptomatic occurrences of UTI among children, pregnant women, diabetics and geriatric populations, diagnosis of which may require collection and testing of several specimens, bacteriuria tests must be sufficiently simple and economical to permit routine performance. Again, this illustrates the need for a rapid and inexpensive bacteriuria detection method.
Current laboratory methods based on culturing microorganisms, e.g., the calibrated loop-direct streak method, require significant incubation periods (18-24 hours) before results can be determined. These laboratory methods are also time-consuming to perform and require considerable clinical training and facilities.
Known methods for the relatively rapid detection of bacteriuria include:
1. Uroscreen.TM. (triphenyltetrazolium chloride) is described in a brochure entitled "A Simple Semi-quantitative Diagnostic Screening Method for Presumptive Bacteriuria" published by Pfizer, Diagnostics Division, NY, 1974. Uroscreen.TM. utilizes a dry, buffered tetrazolium reagent (colorless, soluble 2,3,5-triphenyltetrazolium chloride). In the presence of significant bacteriuria, Uroscreen.TM. will be reduced by the metabolizing bacteria within 4 hours to a pink-red, insoluble precipitate of triphenylformazan. This method has several disadvantages: it may not be accurate because bloody urine includes deposits resembling the pink-red precipitate of a positive test; and highly colored urine (caused by concentration, bilirubin, or drug ingestion) may obscure the results. The accuracy of this test in detecting significant bacteriuria has been reported to be from about 60 to about 90%.
2. Microstix.TM.-3 Reagent Strips for Urinalysis are described in a brochure entitled "Test for Nitrite with Miniaturized Culture Tests for Total Bacterial Gram-Neg Bacterial Counts in Urine," published by Ames Co. (Division of Miles Laboratories, Inc.), Elkhart, IN, 1976. Microstix.TM.-3 is a firm, plastic strip to which three separate reagent areas are affixed, i.e. a chemical test area for the immediate recognition of nitrite in urine and two culture areas for semi-quantitation of bacterial population. The nitrite test, based on a modification of the known Griess nitrite reaction, depends upon the conversion of nitrate (derived from dietary metabolites) to nitrite by the action of certain species of bacteria in the urine. However, a negative result from this test does not provide proof that the urine is sterile. This can be a problem, particularly if there are clinical signs or symptoms to indicate a bacterial infection. Also, blood, Pyridium.TM., bilirubin, methylene blue, and other interferents in the sample may obscure the test results. This method also has several disadvantages inherent to nitrite tests: it must be performed on first-morning specimens for optimum accuracy; it may give false negative results on specimens collected from patients on low-nitrate diets; it can be blocked or interfered with by phenzapyridine hydrochloride or any drug to which the bacteria are susceptible; it requires a large bacterial population for positive results; and it will not detect microorganisms which do not reduce nitrate to nitrite.
3. Montgomerie, J. Z., Kalmanson, G. M., and Guze, L. B. describe the catalase test in "The Use of the Catalase Test to Detect Significant Bacteriuria," Am. J. Med. Sci., 251:94-97, 1966. The catalase test is based on rapid gas production resulting from urea reacting with hydrogen peroxide. This reaction is catalyzed by catalase available from bacteria in the specimen sample. The method has several drawbacks for detecting bacteriuria, however: microoganisms which lack catalase, or those containing low levels of catalase may provide false negative results; and reducing chemicals present in urine capable of reacting with hydrogen peroxide may interfere with the test.
Other diagnostic agents for detecting bacteria in biological and other fluids are described in U.S. Pat. No. 3,496,066 (issued Feb. 17, 1970 to Berger et al) and U.S. Pat. No. 3,621,016 (issued Nov. 16, 1971 to Berger et al). Such agents are metabolized by bacteria present in the sample specimen to produce detectable products.
Hence, there is a need for a simple, reliable and inexpensive procedure for rapid detection of bacteria, and particularly significant bacteriuria, which procedure avoids the problems presented with known procedures.